1. Field of the Invention
The present invention relates to a center electrode assembly included in, for example, an isolator, a circulator, or other suitable device, used in a microwave band, and to a manufacturing method for the center electrode assembly. In addition, the present invention also relates to a nonreciprocal circuit device and a communication apparatus including the nonreciprocal circuit device.
2. Description of the Related Art
An example of a known center electrode assembly used in lumped-constant isolators (nonreciprocal circuit devices) installed in mobile communication apparatuses such as mobile phones, is shown in FIG. 16A. With reference to FIG. 16A, a center electrode assembly 200 includes a microwave ferrite member 201 having a rectangular shape and three central conductors 202, 203, and 204 which cross each other at a predetermined angle on the top surface 201c of the ferrite member 201.
Each of the central conductors 202, 203, and 204 includes grounded leg portions which extend upward from a ground plate provided at the bottom surface of the ferrite member 201. Although only the grounded leg portions 202a of the central conductor 202 can be seen in the figure, the other central conductors 203 and 204 are also provided with grounded leg portions. The grounded leg portions 202a extend along a side surface 201a of the ferrite member 201, are bent at an upper ridge portion 201b, and extend over the top surface 201c. 
In center electrode assemblies used in lumped-constant nonreciprocal circuit devices, the three central conductors are arranged such that the central conductors cross each other at an angle of 120xc2x0 in a rotationally symmetrical manner. This is the condition for reliably making the electrical characteristics of input/output ports, to which the central conductors are connected, stable and symmetrical to each other. In addition, the central conductors are arranged such that the central conductors cross each other at angles shifted from 120xc2x0 when specific electrical characteristics such as insertion loss characteristics and isolation characteristics are desired. In either case, the crossing angle of the central conductors is strongly related to the electrical characteristics so that the crossing angle significantly influences the electrical characteristics. Accordingly, it is extremely important to precisely position the central conductors at a desired crossing angle.
The size of nonreciprocal circuit devices can be effectively reduced by using a ferrite member having a rectangular shape. In such a case, the grounded leg portions of the central conductors are bent at the upper ridge portion of the ferrite member. In order to reliably position the central conductors at the desired crossing angle, it has been suggested to dispose angular points (see 202b in FIGS. 16A and 16B), at which the crossing angle between the central conductors is determined, on the upper ridge portion 201b of the ferrite member 201 in Japanese Unexamined Patent Application Publication No. 2001-60808.
However, due to the differences in thickness and width between each ferrite member, differences between jigs used for bending the central conductors, adjustment errors, etc., the angular points 202b are often displaced from the upper ridge portion 201b and are positioned on the side surface 201a or on the top surface 201c. Especially when the angular points 202b are on the side surface 201a as shown in FIG. 16B, a problem occurs in a process of bending the grounded leg portions 202a at the upper ridge portion 201b. That is, as shown in FIG. 18, when the grounded leg portion 202a is pushed in a direction shown by the arrow A, a bending point 202c is easily displaced to a point 202cxe2x80x2. When such a displacement occurs, as shown in FIG. 17, the central conductors 202, 203, and 204 are displaced from designed positions shown by the dashed lines to positions shown by the solid lines, so that the crossing angle therebetween is also changed from the designed value. Accordingly, desired electrical characteristics cannot be obtained.
In order to overcome the problems described above, preferred embodiments of the present invention provide a center electrode assembly in which the central conductors are reliably disposed at the desired crossing angle and with which desired electrical characteristics can be obtained. In addition, preferred embodiments of the present invention also provide a manufacturing method for the center electrode assembly, a nonreciprocal circuit device, and a communication apparatus.
According to a preferred embodiment of the present invention, a center electrode assembly includes a ferrite member having a substantially rectangular shape and a plurality of central conductors, each of the central conductors including a grounded leg portion which extends upward from a ground plate provided at the bottom surface of the ferrite member along a side surface of the ferrite member, which is bent at an upper ridge portion of the ferrite member, and which extends on the top surface of the ferrite member. The grounded leg portion of each of the central conductors is bent such that the grounded leg portion is substantially perpendicular to the upper ridge portion of the ferrite member, and angular points of the central conductors, the angular points determining the crossing angle of the central conductors, are positioned on the top surface of the ferrite member.
In the center electrode assembly according to preferred embodiments of the present invention, the angular points of the central conductors, the angular points determining the crossing angle of the central conductors, are reliably positioned on the top surface of the ferrite member. In addition, the grounded leg portion of each of the central conductors is bent at the upper ridge portion of the ferrite member such that the grounded leg portion is substantially perpendicular to the upper ridge portion of the ferrite member. Accordingly, the bending point can be prevented from being displaced in the horizontal direction in a bending process, so that the central conductors can be bent at the desired bending angle and the angular points can be prevented from being deformed. As a result, the central conductors are reliably positioned such that they cross each other at the designed crossing angle.
In addition, a manufacturing method for a center electrode assembly according to another preferred embodiment of the present invention includes the steps of positioning the ground plate at the bottom surface of the ferrite member and press-fitting the central conductors inside a concave portion of a mold so that the grounded leg portions are bent and extend along the side surfaces of the ferrite member, and pushing and bending the grounded leg portions at the upper ridge portions of the ferrite member toward the top surface of the ferrite member.
According to the manufacturing method of a preferred embodiment of the present invention, the grounded leg portions of the central conductors are bent such that the grounded leg portions extend along the side surfaces of the ferrite member in a single process. In addition, the central conductors can be positioned on the top surface of the ferrite member at the predetermined crossing angle by merely pushing and bending, toward the top surface of the ferrite member, the central conductors extending upward.
In addition, a nonreciprocal circuit device and a communication apparatus according to other preferred embodiments of the present invention include the center electrode assembly having the above-described characteristics, so that stable electrical characteristics can be obtained.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.